This invention relates to marine powertrains and, more particularly, to a powertrain including a flywheel motor generator operative for battery charging and for engine starting and adapted for powering various accessory loads on a watercraft.
It is known in the art relating to marine powertrains to provide a main engine directly connected through a stern drive or other marine drive unit driveably connected with a propulsion member such as a marine propeller. In a typical system for recreational and light commercial watercraft, the engine may be adapted from an automotive vehicle engine and generally includes a separate heat exchanger system, a belt driven generator connected to charge a 12 volt battery, an engine mounted starter powered by the battery and a controller for operating the system.
To provide power for lights and auxiliary loads such as air conditioning, refrigerator, range, electronic devices and accessories, a separate engine driven 110 or 220 volt AC power generator unit may be provided. A separate 12 volt auxiliary battery may be provided connected with a starter for the power generator engine and this battery may be charged through a converter charger from a 110 or 220 volt source, which may also be used to charge the main engine cranking battery. The auxiliary battery is used for 12 volt loads which may be utilized on the watercraft. The power generator engine typically requires a separate heat exchanger as well as separate fuel and exhaust lines in addition to those provided for the main engine.
The present invention provides a simplified marine powertrain which can avoid the need for a 110 or 220 volt auxiliary generator power unit and separate starter and generator members for the main engine. The powertrain includes a motor generator directly driven by the engine output shaft to which the stern drive or other marine drive unit is also connected. The motor generator provides an AC power output of a specified intermediate voltage (such as 36 volts) that provides adequate power for the intended uses. The output voltage is fed through an inverter to charge an intermediate voltage (36 volt) battery and to power electrical loads. The battery provides power through the inverter to drive the motor generator to crank the engine for starting.
In a preferred embodiment, the motor generator is formed as a so-called flywheel starter generator having a hollow rotor connected through a hub directly to the engine output shaft and mounted within a stationary housing connected to the engine block or frame. A stern drive unit may then be connected to the engine output shaft through the hollow rotor of the motor generator and may extend partially within the rotor if desired.
For operating various accessories on the associated watercraft, the 36 volt battery may be used directly to power 36 volt loads. In addition, a 36 volt to 12 volt DC-DC converter may draw power from the inverter or the 36 volt battery to charge a 12 volt battery useable for operating 12 volt loads on the vessel. Also, a 36 volt to 110 volt or 220 volt DC-AC converter may be operated from the 36 volt battery or the inverter to provide 110/220 volt power for operating AC loads for the various accessories used on the vessel. A system controller may control operation of engine and motor generator controls which may be integrated into an MG module, if desired, for controlling the operation of the various power devices.
By using a flywheel starter generator with a 36 volt or other intermediate voltage storage battery system on a marine vessel, with the motor generator powered by the primary propulsion engine, the following benefits may be realized.
A separate stand-alone 110 v/220 v engine generator with all its associated support systems may be eliminated.
A conventional belt-driven generator on the front of the engine is eliminated, improving packaging of the propulsion engine.
The 36 volt battery may be used to provide substantial electric power for a limited time with the engine off and will provide continuous electric power with the engine running at a low speed. Thus, the battery may act as a secondary source of propulsion power for a backup to the primary system if needed.
The engine and motor generator may also provide primary power for quiet low speed docking maneuvers powering high efficiency electric bow and stern thrusters.
The motor generator can also provide sufficient electric power to support an electrically-driven hydraulic system capable of providing for power steering, trim and other auxiliary hydraulic functions with the engine on or off. This eliminates an engine-driven mechanical pump and simplifies the typical task of marinizing the engine, reducing the boat builder""s cost of various system installations.
The invention also eliminates the traditional marine starter, which is generally mounted in a location where maintenance is difficult.
For improved efficiency, while operating for power generation or low power propulsion, the engine may be provided with a selective cylinder deactivation system which will allow the engine to operate on fewer than all of its cylinders and provide necessary electric power with the engine running slowly in a more efficient mode than with all the cylinders operating.